As treatment using balloon dilation catheters, for example, Percutaneous Transluminal Angioplasty Catheters (i.e., “PTACs”), has progressed into narrower and more remote vessels within the body, this has necessitated the use of catheters having correspondingly smaller shaft diameters and longer shaft lengths. However, this migration towards catheters with smaller diameter, longer shafts has produced several new problems of its own. First, catheter inflation/deflation time performance (i.e., the time required for inflation and deflation of the balloon) has tended to increase in the longer, smaller diameter catheters as frictional resistance to movement of the inflation fluid through the balloon inflation/deflation lumens of the catheter becomes significant. Second, accessing increasingly smaller body lumens requires that the distal portion of the catheter shaft have sufficient lateral (i.e., side-to-side) flexibility to follow the guidewire as it twists and turns through the smaller, more arduous pathways in the body. If the distal end of the catheter is not flexible enough, it may pull the guidewire out of position in the target lumen rather than follow it. The flexibility of the distal portion of the catheter is often referred to as the “trackability” of the catheter.
In a rapid-exchange type catheter, the guidewire does not run through the entire length of the catheter shaft, but rather runs parallel to the shaft for the majority of it's length, then enters the shaft through a side aperture and runs through only the distal portion of the shaft and the dilation balloon. The side aperture region has a reduced cross section that tends to be a weak point in the structure, and reinforcement in this area is often required. However, the reinforcement necessary to support the side aperture area tends to make the distal portion of the shaft so stiff that it has insufficient trackability.
A need therefore exists, for a rapid exchange balloon dilation catheter (and shaft therefor) with improved trackability in the distal portion. Preferably, the trackability will increase toward the distal end of the shaft.